1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to an apparatus for controlling color registration sensors by incorporating the registration sensors into a transfer unit and using characteristics of the registration sensors stored in a memory and a method thereof.
2. Description of the Related Art
Generally, an electro-photographic image forming apparatus, such as a color laser printer, includes four photosensitive drums, an exposing unit, developing units, and a transfer belt. The photosensitive drums correspond to four separate colors: yellow, cyan, magenta, and black. The exposing unit forms an electrostatic latent image that a user wants to print by irradiating light. The developing units develop the electrostatic latent image by using developers for the respective colors. The transfer belt sequentially and reiteratively receives an image which is developed onto the respective photosensitive drums to form a complete color image, which is then transferred to a sheet of paper.
In order to obtain an accurate color image, starting and ending points where the transfer of the electrostatic latent image, or a toner image, on a transfer belt start and end must be aligned in accordance with the respective colors. Therefore, it is important that exposure starting points in accordance with the respective photosensitive drums of the exposing unit are accurately controlled by taking a transfer speed of the transfer belt into consideration. Here, the accurate setting of the exposure starting points is referred to as registration. In order to achieve the registration, the registration sensors irradiate light onto a test pattern of the transfer belt and sense the amount of reflected light.
A conventional registration sensor is placed into a set frame of an image forming apparatus instead of the transfer belt. However, due to mechanical design constraints, however, the registration sensor is placed at the top of a fuse unit, which may lead to heat generation and a breakdown or error of the registration sensor. In addition, a problem exists when the registration sensor is placed into the set frame of the image forming apparatus. Therefore, left-right precision of the registration sensor must be maintained. In addition, because of a structural height variation and characteristic differences stemming from the sensitivity of light emitting and receiving units of the registration sensors, output characteristics of the registration sensors need to be gradually corrected, which can be a time-consuming process.
Accordingly, there is a need for an improved method and apparatus for controlling color registration sensors based on characteristics of the registration sensors.